Grease composition



Oct. 14, 1952 R. J. MOORE ET A1. 2,614,077

GREASE COMPOSITION Filed Dec. 27, 1949 Fxe. I

nvenib a Roberi' J. Moore 'This property is A'bearing greases, for example. The ability of the Patented Oct. 14, 1952 Berkeley, Calif., assignors to Shell Development Company,Y SanFrancisco, Calif.; a corporation of Delaware vapplication December 27, 1949, serial No 135,124

'9 claims. (c1. 25e-3am This invention is concerned with the preparavti'onof greases having improved mechanical stability. More particularly, it is directed to grease compositions containing' particular classes `of agents imparting mechanical stability to greases. In the prior art, numerous lubricating grease compositions have been proposed having various characteristics such as high temperature sconsisten'c'y, resistance to syneresis, resistance to oxidation, water-resistant properties, and 'the jlike. lAsa general rule, such'conipositions have 'been prepared by incorporating `in 'a suitable lubricating oil metallic soaps of fattyoils or' fatty acids which have the property of thickening' the lubricating `oil'toa grease-likeconsistency. In 4many applications of lubricating compositions, thecOnditions of use are such that'liquid com- 'positions are unsatisfactory because they runout ,of bearings 'or otherv parts' to be lubricated or they are Washedaway readily or otherwise rendered ineffective Oneof the important characteristics 'of greases comprises the ability of the composition to maintain its consistency' at high temperatu'res and over V extended 'periods of use. particularly important in ball grease to maintain its original consistency can 'bevtested'by w'ellknown'methods which comprise 'working the grease under standardized condiv:tions 'and periodically testing' its penetration.

1 Y' The mechanical stability of various greaseshas `'been' found to'vary widely depending principally upon the predominating soap used 'for gelling the grease. Lithiu'mst'earate grea'sesc for example,

have been found to have relatively poor mechanical stability. A substantial improvement maybe 'made'lby substituting, in Whole or inv part, thefatty acid soap by a soap of a`hydroxy fatty 'acid' such as 1'2'hydroxystear`ic acid and corresponding n acids derived from natural sources such'as from hydrogenated castor oil-` Where evenhigher resistanceto the adverse inuence of? the' continuous Wo'rking or' elevated temperaf'ture 'is desired, even the soaps of the hydroxy fatty acids of the character describedabove have been found to =be inadequate.

v It is anvobjectfof-t-he' 'present invention to provide greases v lhaving Vimproved mechanical staubility.v It -isy another-object ofthe present invention to provide l greases-havingimproved 'mechanical stability at A,el-:vated temperatures, 1t

:is a further `objecty of' the present' inventio no 'polar groupsoth'er than` the carboxy va criticallyA defined range of"ratios,"ha`ve uts'tanding structural stability. `'The 'majorj soap is a lithium soap of an aliphatic monocarb ylic acid'having 10 to 24 rcarbon, atoms and vv"g ,D- The'minor soap "is that of amonocarboxyhcacid having' 3 to 18 carbon atoms and "bearinga hydrogen Ybonding substituent less than'lllbarb'on atoms removedfrom the carboxyl group LIn order to attain the outstanding -s'tructura bility with which this invention V`isconce-r ed, the normal Ypercentage of themin'orsoap ust ybe :between 4 -and V12 lmole per cent, and pre erably, isbetween 5 and l-mole'per'fcent, based-'on the total soap content of the'lgrease. 'f

Thefstalilzingl additives Within the pn'lll/'evv'f the present invention comprise'soa'ps of'f-r e 'monocarboxylic acids, cycloalkane mono arlboxylic-'acids and monocyclic aromatic monocarboxylic acids,` each of-which contains faihyd''o'- lgenfbonding or co'`o'rdinating substituent 'Yle's's thang carbon-`atoms removed from the carboxyl =group. The preferred additives which `have mbeen found to be especiallyuseful l'in' the present .com-

monocarboxylic'iacids, the monocycloalkane hydroxy monocarboxylic acids and-monocycloaro matic hydroxy'monocarboxylic acids. Still-'other preferred grease additives #comprise soapsiof monoketoalkane Imono'carboxylic .acids and-monoaninoalkane monocarboxylic` acids :whereinthe keto or amino groups areat'tachedto carbon atoms less than 9 carbon atoms removed vfrom the carboxylic acid-group. s s

lWhile the lithium soaps are preferredin'ith'e present compositions, otheralkali-metals vsuch as sodium'and'potassium maybe employed., 'The class of compounds hav-ing outstandingfeiectiveness in this respect comprises the lithiunrsoa'ps of monohydroxy alkane monocarboxylic :facids having -fromv3wto-18- carbon atoms wherein the hydroxyl groupgis" in the beta, gamma lordelta, positions with respect vto the carboxyl group,

such-as hydroxy propionic acids, hydroxybuty-ric acids, hydroxy valerio acids, hydroxy caproic acids, hydroxy enanthic acids, hydroxy caprylic acids, hydroxy lauric acids, hydroxy myristic acids, hydroxy palmitic acids, hydroxy stearic acids, and hydroxy arachidic acids, as well as their homologues and analogues. The corresponding mercapto acids wherein the hydroxy group is replaced by a mercapto group function in a similarly effective manner in the present compositions.

Anotherl effective group of stabilizing agents comprises the vmonoaminoalkane monocarboxylic acid soaps and especially the lithium soaps of acids such as 3-aminopropionic acid, 3-aminohexanoic acid, -aminopentanoic acid, Li-aminohexanoic acid, 5aminodecanoic acid, as well as their analogues and homologues. It is preferred that aminoalkane acids having from 3 to 18 carbon atoms be employed and substantially unbranched acids are preferred.

Metal soaps of monoketoalkane monocarboxylic acids having from 3 to 18 carbon atoms may be used in the subject greases. These may be lithium, sodium, calcium, aluminum or potassium soaps of acids such as pyruvic acid, propionyl I carboxylic acid, acetoacetic acid, levulinic acid and acetobutyric acid. The corresponding thio acids wherein the oxygen atom of the keto group is replaced by asulfur atom similarly function as stabilizers in the present greases.

Av particular type of desirable stabilizer comprises a soap of hydroxy naphthenic acids such as those derived from petroleum sources. It will be 4appreciated that a mixture of this type is more clearly defined by a source than by its exact structure. However, the hydroxy naphthenic acids which are found to be eiective in the present compositions are understood to be predominantly hydroxy allrylated cyclopentanoic acids, a large proportion of which comprises hydroxy derivatives of (3-ethyl-e-methyl-l-cyclopentanyl) acetic, butyric and valerie acids. Of course, the pure, clearly dened individual members of this class may be employed if desired. However, mixtures of hydroxy naphthenic acids derived from petroleum oils, when saponied `with an alkali metal, function as satisfactory stabilizing agents in these compositions.

The soaps of the aromatic acids which function as mechanical stabilizing agents in the present compositions comprise especially those of monocyclic aromatic monocarboxylic acids bearing a hydrogen bonding or co-ordinating substituent such as a nitro, amino, mercapto, hydroxy, keto, sulfo or thiol group attached to the aromatic ring or to a short side chain thereon. Typ- `ical suitable soaps of this description include the sodium, potassium, aluminum, calcium or lithium soaps of ortho, meta, or para-nitrobenzoic acid; ortho, meta, or para-aminobenzoic acid; ortho, meta, or para-thiolbenzoic acid; ortho, meta-, or para-hydroxybenzoic acid; mandelic acid, tropic acid, benzoyl formic acid and benzoyl acetic acid.

The soaps which function as outstanding stabilizers in the present compositions include those such as described above, especially those of the substituted alkane acids having substantially no branching in the hydrocarbon portion of the molecule as well as the cycloalkane or aromatic acids bearing a minimum of branched chain substituents. The examples appearing hereinafter .indicate that the position of the hydrogen vbonding or co-ordinating substituent with respect to the carboxyl group is immaterial as long as it is 4 dependent from a carbon atom less than 9 carbon atoms removed from the carboxyl group. If a greater space exists between the two functional groups, the enhanced mechanical stability of the grease correspondingly suffers.

The class of gelling agents in the greases under consideration comprises the lithium soaps of aliphatic monocarboxylic acids having from l0 to 24 carbon atoms said acids containing no polar substituents other than the carboxyl group. These include especially the mixtures of fatty acids derived from natural fatty oils such as vegetable oils, animal oils, and sh oils. Hydrogenated vegetable oil acids have been found to be especially useful. Other suitable acids include oleic acid, stearic acid, linoleic and linolenic acids, as well as the acids derived from beef fat, tallow and the like.

The lubricant comprising the base of the grease will, in most cases, be a mineral lubricating oil. However, natural oils such as vegetable oils or animal oils may be employed as well as synthetic lubricants such as polymerized olefms, polyalkylene oxides such as polypropylene oxide, polymerized suldes such as polypropylene sulfide, polymerized glycols such as polypropylene glycol, esters of dicarboxylic acids such as bis-(2-ethylhexyl) sebacate and phosphates such as tributyl phosphate or tricresyl phosphate. In cases where high temperature use is contemplated, fluoro compounds and the hydrocarbyl silicones may be used in whole or in part.

The respective quantities of each of the principal ingredients may be varied within exible limits except for the required range of ratio of the stabilizing soaps to the principal gelling soaps. While the addition of the stabilizing soaps such as those of 4-hydroxyvaleric acid to soaps such as lithium stearate causes a certain amount of increased mechanical stability, it has been discovered that only within strictly limited ratios an unexpected and surprisingly great increase in mechanical stability is attained. To illustrate this, reference is made to the ligure of the drawing accomanying this specification. The figure proves that a critical relationship exists when the stabilizing additives are present in ordinary fatty acid soap greases such as lithium stearate grease. The mole percentage of the additive soap should be between 6 and 12 mole per cent of the total soap content.

The total soap content of the greases may be from about 4 to 25% by weight of the total grease, preferably the soap content is between 7 and 20% by weight of the grease. It will be understood that mixtures may be employed in the case of each of the three principal components. For example, when a low temperature grease is required, up to about 20% by weight of the oil base component is desirably an ester of a dicarboxylic acid such as bis-(2-ethylhexyl) sebacate in admixture with mineral oil. Mixtures ot either pure or natural soaps for both the principal gelling agent and for the stabilizer may be used. Other ingredients which may be present in the compositions comprise glycols such as glycerine, for the prevention of bleeding and the like, and anti-oxidants such as para-phenylene diamine. In many instances, additives o1' this type are found to be unnecessary since the described classes of stabilizing soaps have been found to improve not only the mechanical stability of the grease compositions but also its resistance to bleeding and oxidation.

The preparation of the subject greases preterably" follows thief-.processes desoribedin. prior art literature .with certainnprecautions.taken toravoid dehydrationl of the hydroxyrstabilizing agentsfor loss of the other. types. offhyd'rogen; bonding-substituents detailed above: Atypical preparation of lithium greases comprises. saponii'lcationot the two vclassesof carboxylic acidsgnamely, the major grease'y forming. fatty acid and the stabilizing acid, dehydration of the soap in the presence of av portion ofthe oil, solution ofthe soapin oil by Yheatinegand cao-precipitation of the two soaps inthe desiredfib'er formby lowering theftemperature; preferably together with stirring: and working;

More: particularly, it has'- been. found? that greases having optimum consistency,N are` prepared-.by mixing .theitwo' typesV of acids .with 'about cnet-third of theoil,A adding lithium hydrate at about. 100" C., then". raising thei. temperature. to abouti200,?C`.` in order to dehydrate:- theconcentrated soap'. mixture and to'. dissolvey the-.soap in the oil. The concentrate is then quenched.' by the: incorporation.. of the remaining/'portion' of cold. oil. Thef mixture is reheated to about 190* C.. and finally cooled to. room temperature with;.worl 'ing.

The step: of dehydration is carried out-4 under conditionswhich will' removewater which has been introducedtogether with the lithium hydroxidebut.heating iscontrolled', as already indicated, ata temperature lower'thanithe dehydrating temperture of. theihydroxy fatty "acid or corresponding decomposition temperature; of the otherv stabilizing additives. Ifzthe dehydrating temperature is. raised 'above-about 230 C., rmost of the.` stabilizing additives will. gradually lose their hydrogen bonding substituents and form decompositionv products principally comprising unsaturated acids or their. soapssuch as the soaps. oil acrylic acids or methacrylic acids.; or their higher..A homologues. These unsaturated decomposition4 products; While Ahaving, certain benecial eiectswhen present in .largeamounts do not-have a benecialeffect uponthe mechanical stability-of greases as `descrbedfherein. when present VVwithin the critically deiinedv ratio based on the totalsoap content.. Hence, one feature of the present. inventioni comprises a process. of forming. the greases of thel components A discussed above including thestep of removing Water. from the grease-.at a temperature.V below thedecompositicn temperature. of the; stabilizing, additives defined .in the yforegoing, disclosure.

While the mixture of soaps may be preformed and subsequently addedt to. theoi-l in order. to form a grease, it has been found `thatathe quench system.. provides a grease n having far better mechanical stability and, hence; the foregoing describedv type of formation. should, be used whenever. possible.

While various types of mineral oil may be. used in the preparationof-the:greases of thepresent invention, it.has been found that the-more highly refined oils,.preferably highly paraiinic and/or naphthenic oils, result in greaseshavingA improved mechanical stabilitywhen the subjectedditives are. present. Furthermore, thenitrogen contentiof. the rened oil should be as low as possible. Lubricating oils having from to 25% aromatics are. especiallysatisfactory for the present compositions, althoughthe preferred range .of aromatic content. is that statedfhereinbefore.

The mechanical stabilityy of thegreases produced. in.. accordance with the present .invention may f be 1 tested with. thel Shell Roll Tester; cur- 6. rentl'yused: extensively in thegrease-industry. The apparatus in. which. the. test' is madev is'a simulated roller bearing'andconsi'sts of.' a1 horizontal 31/2` inch hollowv cylinder, 'l'inche'slongz into which there is placed a solid steel cylinder 21/4 inches in diameter and about 'l inches long,

weighing approximately 11 pounds. The' largerv cylinder, initially closed at lone end, has a cap placed over the open end after the grease has beenintroduced. Enough clearance is permitted for the solid steel cylinder to roll freely inside the larger cylinder which is rotated at 160 R. P. M., and the solid cylinder rotates; therein by means of contact with the inside-of the larger hollow cylinder. In an apparatus of this char.:- acter, a given amount of. greasemay be. rolled for aperiodof time. and testedforv consistency` to obtainthe. degree of.' mechanical stability ofthe grease. The smaller4 cylinder rolls, works. and masticates. the grease thoroughly during' thetest. At giventime intervals, the greaseisremoved testedfor consistency and. then replaced in thel apparatus. for further working.

The, consistency of the grease is. determined by means ofV a special small cone attachedto the' regular ASTM'penetrometer. A small cup isv used'in conjunction with the test. Theworked penetration obtained by this apparatus'. is referred to herein as micro penetrationlwhich may be correlated, if desired,'with the regular ASTM' penetration by means oa previously de.- termined curve. The roll stability of. a grease comprises. the time requiredfor rolling in. the above apparatus for the grease to reach a maximum micro penetrationy of- 230 dmm.

While themechanical stability of greases; at room temperaturev is important, it is alsoimperative that greases have suilicientA stability at ele.- vatedtemperatures if they are to be. usefuLin apparatus running at aboutlOO. C. or even higher. Lithium` soap greases are notorious for their poor stability, at. elevated temperatures- It. has

been'found that the` present additives. if they occur in the greases within the criticalconcen.- tration range. discussed above,. stabilize the greases. sufliciently to permit their use for as much as thirteen times as long a service. period as when the unstabilized grease is utilized.

EXAMPLE I In the following tests` hydrogenated:l sh oil acids .Wereemployed These are essentially mixtures. of'.- fatty acids with a predominating proportion ofY stearic acid, and?r appreciable proportionsof other fatty acids'having' from lllstol22 carbon atoins..y .Thebase oilrwas a turbineoilfof low aromatic cont'entand: had :at-.viscosity of 100 centistokes at witha viscosity indexof 55. One-third of the oil'was mixed with thefsh oil acids or With fish oil acids and stabilizing acids in proportions to yield a nnal grease having 'a total of 8% by weighttotal soap containing 0.3' Weight per. cent. (8;6 vmole per cent) ofthe stabilizing agent, based on the total composition. Lithium hydrate was added to thev mixture.` at 100 C. in stoichiometric amount to neutralize the'v acids,. afterr which the Ysoap-oil.- concentrate wasV dehydratedy at 200 C. The remaining-1 oil wasthen. added: and the mass heated .to 205-210 C. to dissolvethesoaps. They mixture was' allowed to1co`oir1'statically to 120 C., held at this temperatureifor. two hoursl and. then allowed.v to cooltoiroomtemperaturez. The cooled gel-was thenworkedwith an ASTM grease'l worker to obtain,agre'asesuitablerfor testing-.1

7 The greases prepared by the above process were tested for mechanical stability in the Shell R011 Tester as described hereinbefore. The data in the table show the elfect of various additives.

Table EFFECT F ADDITIVES ON MECHANICAL STABILITY OF LITHIUM STEARATE GREASE An additional feature of the compositions of the present invention comprises the advantage gained with respect to aeration during milling. Under the ordinary conditions of grease milling large amounts of air are incorporated in the grease which must be subsequently removed under vacuum or by some other suitable means. The unmodied grease described above gained 40% in volume during the milling operation. In contrast to this, when any of the other samples containing the stabilizing additives described were milled, the gain in volume due to aeration amounted to about only 4% to 6%. The reason for this improvement in operating characteristics is not obvious at the present time, but the amount of aeration may reflect the formation of extremely ne soap particles by attrition which then function to form an air-oil emulsion.

EXAMPLE II Hydrogenated fish oil acids are mixed with 6 mole per cent of alpha-amino-isocaproic acid and mineral lubricating oil. A mixture of soaps is obtained by neutralization of the components with potassium hydroxide. Neutralization is effected by heating a mixture of oil, hydroxide and acids. The composition may be dehydrated at a temperature of about 10D-200 C. Sufficient additional oil is added and the mixture is milled to give a grease having a total soap content of about 10%. Greases prepared in accordance with this procedure have excellent mechanical stability.

We claim as our invention:

1. A lubricating grease having approximately the following composition:

Approximate weight per cent Mineral lubricating oil 92.0 Lithium soaps of hydrogenated fish oil acids 2. A lubricating grease having approximately the following composition:

Approximate Weight per cent Mineral lubricating oil 92.0 Lithium soaps of hydrogenated sh oil acids 7.7 Lithium soap of 4ketovaleric acid 0.3

3. A lubricating grease composition containing only carboxylic acid soaps as gelling agents comprising a major amount of a mineral lubricating oil having an aromatic hydrocarbon content between 0 and 25% by weight and between 4 and by weight of a mixture of alkali metal soaps of aliphatic monocarboxylic acids, at least one of said soaps being a lithium soap of an acid having from 12 to 24 carbon atoms and bearing no polar substituents other than the carboxyl group and at least another one of said soaps being an alkali metal soap of an acid being a hydroxy fatty acid having from 3 to 18 carbon atoms, wherein the hydroxy substituent is less than 9 carbon atoms removed from the carboxyl group, said hydroxy fatty acid soap constituting from 4 to 12 mole per cent of the total soap content.

4. A lubricating grease composition containing only carboxylic acid soaps as gelling agents comprisinga major amount of a mineral lubricating oil, 4 to 25% by weight of the grease of a mixture of lithium soaps of fatty acids, at least one of said acids having from 12 to 24 carbon atoms. and at least another one of said acids being s. hydroxy fatty acid having from 3 to 18 carbon atoms, the hydroxy substituent being less than 9 carbon atoms removed from the carboxyl group, said soaps of the hydroxy fatty acid constituting between 5 and 10 mole per cent of the total soap content.

5. A grease composition containing only carboxylic acid soaps as gelling agents comprising a lubricating oil, 4 to 25% by weight of a. mixture of lithium soap of an aliphatic monocarboxylic acid having 10 to 24 carbon atoms bearing no polar groups other than the carboxyl group, and an alkali metal soap of an aliphatic monocarboxylic acid having 3 to 18 carbon atoms bearing a hydrogen bonding substituent less than 9 carbon atoms removed from the carboxyl group, the second soap being present in an amount between 4 and 12 mole per cent of the total soap content, said hydrogen bonding substituent being one selected from the group consisting of hydroxy, keto, amino, nitro, mercapto, thiol and sulfo groups.

6. A grease composition containing only carboxylic acid soaps as gelling agents comprising a lubricating oil, 4 to 25% by Weight of a mixture of lithium soap of an aliphatic monocarboxylic acid having 10 to 24 carbon atoms bearing no polar groups other than the carboxyl group, and an alkali metal soap of a monocarboxylic acid having 3 to 18 carbon atoms bearing a hydrogen bonding substituent less than 9 carbon atoms removed from the carboxyl group, the second soap being present in an amount between 4 and 12 mole per cent of the total soap content, said hydrogen bonding substituent being one selected from the group consisting of hydroxy, keto, amino, nitro, mercapto, -thiol and sulfo groups.

7. A grease composition, containing only carboxylic acid soaps as gelling agents, comprising a lubricating oil and from 4 to 25% by weight of a mixture of a lithium soap of a fatty acid having from 10 to 24 carbon atoms per molecule and a lithium hydroxy propionate, the latter being present in an amount between 4 and 12 mole per cent of the total soap and salt content.

8. A grease composition, containing only carboxylic acid soaps as gelling agents, comprising a lubricating oil and from 4 to 25% by Weight of a mixture of a lithium soap of a fatty acid having from 10 to 24 carbon atoms per molecule and a lithium soap of a keto fatty acid having from 3 to 18 carbon atoms per molecule, the keto group being less than 9 carbon atoms removed from the carboxyl group, the latter soap being present in an amount between 4 and l2 mole per cent of the total soap content.

9. A grease composition, containing only carboxylic acid soaps as gelling agents, comprising a lubricating oil and from 4 to 25% by Weight of a mixture of a potassium soap of a fatty acid having from 10 to 24 carbon atoms per molecule and a potassium soap of an amino fatty acid having from 3 to 18 carbon atoms per molecule, 5 the amino group being less than 9 carbon atoms removed from the carboxyl group, the latter soap being present in an amount between 4 and 12 mole per cent of the total soap content.

ROBERT J. MOORE. WALFRID SAARNI.

10 REFERENCES CITED The following references are of record in theI iile of this patent:

UNITED STATES PATENTS Number Name Date 2,450,254 Puryear et al Sept. 28, 1948 2,455,892 Fraser Dec. 7, 1948 2,468,098 Morway et a1 Apr. 26, 1949 10 2,487,080 Swenson Nov. 8, 1949 

5. A GREASE COMPOSITION CONTAINING ONLY CARBOXYLIC ACID SOAPS AS GELLING AGENTS COMPRISING A LUBRICATING OIL, 4 TO 25% BY WEIGHT OF A MIXTURE OF LITHIUM SOAP OF AN ALIPHATIC MONOCARBOXYLIC ACID HAVING 10 TO 24 CARBON ATOMS BEARING NO POLAR GROUPS OTHER THAN THE CARBOXYL GROUP, AND AN ALKALI METAL SOAP OF AN ALIPHATIC MONOCARBOXYLIC ACID HAVING 3 TO 18 CARBON ATOMS BEARING A HYDROGEN BONDING SUBSTITUENT LESS THAN 9 CARBON ATOMS REMOVED FROM THE CARBOXYL GROUP, THE SECOND SOAP BEING PRESENT IN AN AMOUNT BETWEEN 4 AND 12 MOLE PER CENT OF THE TOTAL SOAP CONTENT, SAID HYDROGEN BONDING SUBSTITUENT BEING ONE SELECTED FROM THE GROUP CONSISTING OF HYDROXY, KETO, AMINO, NITRO, MERCAPTO, THIOL AND SULFO GROUPS. 